The starting-point for this presentation is St John Chrysostom’s definition of prophecy in the introduction to his commentary on Jeremiah. The definition was obviously considered normative in Byzantium, because it was reproduced almost word for word by two ‘encyclopaedic’ works of the 9th and 10th centuries. The binary opposition that Chrysostom formulated between “spiritual prophecy” and “diabolical prophecy” represented the official attitude of the Byzantine church. It was applied by ecumenical councils and local synods, and it systematically developed by the 12th-century canonists, above all Theodore Balsamon, into an absolute condemnation of all sorts of divination. But in reality things were rather more ambivalent reality. On the one hand, divination often took on a Christian appearance through the use of sacred language and symbols, the participation of monks and clergy, a tendency to syncretism among Byzantine intellectuals, and a long tradition of Christianising the practice of astrology on the basis of Genesis 1, 14. On the other hand, the existence charismatic, spiritual prophecy in contemporary society was not recognised outside the closed, circular discourse of hagiography, which insisted that every prophet had to be a saint and every correct prophecy was a proof o sanctity. Other sources present predictions by self-styled holy men in neutral or hostile terms. Neither Chrysostom nor Balsamon presents any contemporary example of divine prophecy. For Chrysostom, the model of legitimate prophecy lay in the past and in the Old Testament, and true prophecy was a threat of divine punishment that could be averted by repentance. For Balsamon, the prophecy of ascetic monks was indistinguishable from the divination of soothsayers and ‘wise old women’. Byzantine literature has left us two vivid portraits of ambivalent prophets who were consulted by the authorities: the visionary Dosithea described by Michael Psellos in his indictment of the patriarch Michael Keroularios, and ‘Father Basilakios’ at Raidestos as described by Niketas Choniates in his account of the downfall of Isaac II (1195).